I have no ideas about the possible involvement of RM but I am very skeptical that this was an accident. Rear ending a bicycle at night would be unusual because directly in the path of the vehicle is the place that an object would be clearly visible. Of course, if he were drunk or not paying attention, anything is possible.
If the bicycle were hit squarely from behind, what would happen would be that the bicycle would accelerate to the speed of the vehicle while the rider would continue moving forward at the speed she was riding. Hand grips might come off in her hands. Within a fraction of a second, the front of the vehicle; probably the grill, would hit the rider in the back and probably the back of the head. The rider would then either roll up on the hood or, with a large pick-up with a high front grill, drop under the vehicle and be run over. The front bumper would probably pick up some transfer from the bike but otherwise be undamaged. The grill and/or headlights, however, would almost certainly receive some damage.
The rider would probably not suffer heavy bleeding but there would be some cuts and abrasions. There would be some blood at the scene. The bigger indication of the accident would be debris. Plastic and glass would scatter as well as contents of her knapsack and possibly articles of clothing. The bike might travel 20 to 30 feet forward. The riders injuries would include closed head injury and possibly internal bleeding which would both be life threatening but would probably not be fatal instantly. Most deaths from head injuries result from the swelling of the brain due to gradual bleeding. This can take hours or even days.
Most likely, the driver would be confronted with a seriously injured girl, a damaged bike and a certain amount of debris. If he isn't going to confront the consequences of his action and call 911 or go to the Circle K for help, just taking off, the standard Hit & Run is the obvious course of action.
The decision to collect the injured girl, the bike and all of the debris would take precious time that anyone might come along and see it. More importantly however, even if the rider were dead, the driver, who I would assume had no medical training, would not be certain. Even a drunken sociopath would understand the implication of taking a seriously injured rider and dumping her body somewhere to die: he would go from vehicular manslaughter (at worst) to First Degree Murder. Someone might take this route if they had a chance to think it all out, but on the fly? Never.
Now, he could claim he was transporting her to the hospital, but he "panicked" when she was DOA, but why would he have taken the bike as well? It will not fly, but it might be a desperate ploy at his trial.
I am quite sure this was deliberate "bump and grab" sexually motivated attack.
Somehow, I find 19 to be very young for this sort of attack. Using a vehicle as weapon seems like something someone who wasn't real confident of their physical strength might pull. I'm sure we will be finding out more soon enough.
